The present invention generally pertains to telecommunications and is particularly directed to relaying communication signals from originator user terminals to destination user terminals.
Communication signals are relayed from originator terminals to destination terminals by relay terminals. Relay terminals may be disposed in towers, communication satellites and/or aircraft. Typically, the user terminals are ground-based.
In the prior art, relay terminals that simultaneously receive a plurality of communication signals for relay to a plurality of destination terminals operate either as “bent pipe” relays, or as “processing” relays with fixed channel assignments. With “bent pipe” relays, the received signals are repeated directly to either the destination terminals, or to one or more gateway terminals for further processing. Control of access to bent pipe relays is only by administrative means. Examples of systems using bent pipe relays include Inmarsat, Globalstar, and DSCS-III.
With processing relays, multiple channels are established by onboard processing. These channels are separated on the uplink by the onboard processing relay, such as by channel filtering, or dehopping of frequency hopping signals, and demodulation/decoding. The data streams of the various uplink-processing channels are switched to the downlink paths, and then encoded and modulated for transmission via the downlink to the destination terminals. With on-board processing, relay access is achieved by any terminal having the appropriate combination of time/frequency spectral occupancy and modulation/coding. In the prior art, the relationship between the established uplink channels and the downlink channels is determined by quasi-static connections stored in an onboard data table in the relay terminal. In processing relay systems, uplink receivers, demodulators and decoders, and downlink coders, modulators and transmitters, are assigned to specific channels on a quasi-static basis. Examples of systems using processing relays include Iridium, Thuraya, AceS, and Milstar.
In many of the satellite relay systems using either bent pipe relays or on-board processing, a given user may use a special access request channel to request the assignment of a communications channel. Access requests are serviced by a ground-based control station and are fulfilled by assignment of a communications channel. The channel assignments are distributed to the requester and any other users that may be involved in the communications; and commands that are sent up to the satellite relay terminal configure the payload switching/routing and other signal processing that are incident to relaying of the communications signals that are received by the relay terminal.
In both classes of systems, the antenna system may have multiple beams, each with individual relay or processing capabilities, and different coverage areas. The assignments among the beams and the relay/processing capabilities are also static or quasi-static.
Blockage of propagation paths substantially constrains the reliability of relaying by airborne or space-borne relay terminal. Previous approaches to provide deliberate path diversity, with appropriate combining to increase the likelihood of proper reception, include MUBLCOM and Globalstar. In the MUBLCOM approach, a combination of coded frequency hopping signals, bent pipe relays (with some interference suppression processing), and multiple independent receivers for reception of relayed and direct path signals, and non-coherent combining, provides for direct user-user reliable communications via whatever paths are available. In the Globalstar approach, a combination of coded direct sequence signals, bent pipe relays, and hub processing, and coherent combining of available relayed signals, provides cellular-like communications between mobile users to (via the hubs), the ground infrastructure or other mobile users. A limitation of the MUBLCOM approach is that the relays do not reject interference, and do not provide positive control of access to the relay resources. Limitations of the Globalstar approach are that the relays do not reject interference, accurate real-time power control must be achieved to maximize capacity, and control of access and relaying are performed through hubs.
In the prior art, relay terminals that simultaneously receive a plurality of communication signals for relay to a plurality of destination terminals forward service requests that include user terminal identification codes to terrestrial gateway control terminals, which process such service requests in combination with stored authorization data to determine a priority in which the received communications signals are relayed to the respective destination terminals. Typically, different frequency-hopping patterns are applied to the respective relayed signals; and depending upon the relative positions of the relay terminal and the destination terminals some of the communication signals may be relayed within different beam paths.